Many anatomic structures in the mammalian body are hollow passages with walls of tissue that define a central lumen, which serves as a conduit for blood, other physiologic fluids, nutrient matter, or waste matter passing within the structure. In many physiologic settings, dysfunction may result from a structural lumen which is either too large or too small. In most such cases, dysfunction can be relieved by interventional changes in the size and/or shape of the lumen.
As a result, there is often a need to adjust the size and/or shape of the internal circumference of an orifice or other open anatomic structure in order to achieve a desired physiologic effect. Such surgical procedures often require interruption of the normal physiologic flow of blood, other physiologic fluids, or other structural contents through the orifice or structure. However, the exact amount of change in the size and/or shape of the orifice or structure needed to obtain the desired effect usually cannot be fully appreciated until physiologic flow through the orifice or structure is resumed. It would be advantageous, therefore, to have an adjustable means for achieving this change in the size and/or shape of an orifice or structure, such that the adjustment could be made after its implantation, and after the resumption of normal physiologic flow in situ.
One example of dysfunction within an anatomic lumen is in the area of cardiac surgery, and, specifically, valvular repair. Due to the difficulties in engineering a perfect prosthetic heart valve, there has been a growing interest in repairing a patient's native valve. In particular, mitral valve repair has become one of the most rapidly growing areas in adult cardiac surgery today.
Historically, most valvular pathology was secondary to rheumatic heart disease, a result of a streptococcal infection, most commonly affecting the mitral valve, followed by the aortic valve, and least often the pulmonic valve. The results of the infectious process are mitral and aortic stenosis, followed by mitral and aortic insufficiency. With the advent of better antibiotic therapies, the incidence of rheumatic heart disease is on the decline, and accounts for a smaller percentage of valvular heart conditions in the developed world of the present day. Commissurotomy of rheumatic mitral stenosis was an early example of commonly practiced mitral valve repair outside the realm of congenital heart defects. However, repairing rheumatic insufficient valves did not provide good results because of the underlying valve pathology and the progression of disease.
Most mitral valve disease, other than rheumatic, results in valvular insufficiency, which is generally amenable to repair. Chordae rupture is a common cause of mitral insufficiency, resulting in a focal area of regurgitation. One of the first successful and accepted surgical repairs was for ruptured chordae of the posterior mitral leaflet. The technical feasibility of this repair, its reproducibility, and its long-term durability led pioneer surgeons in the field of mitral valve repair to attempt repairs of other valve pathologies.
Mitral valve prolapse is a fairly common condition that leads over time to valvular insufficiency. In this disease, the plane of coaptation of the anterior and posterior leaflets is “atrialized” relative to a normal valve. This problem may readily be repaired by restoring the plane of coaptation into the ventricle.
The papillary muscles within the left ventricle support the mitral valve and aid in its function. Papillary muscle dysfunction, whether due to infarction or ischemia from coronary artery disease, often leads to mitral insufficiency (commonly referred to as ischemic mitral insufficiency). Within the scope of mitral valve disease, this is the most rapidly growing area for valve repair. Historically, only patients with severe mitral insufficiency had their mitral valve repaired or replaced, but there is increasing support in the surgical literature to support valve repair in patients with moderate insufficiency that is attributable to ischemic mitral insufficiency. Early aggressive valve repair in this patient population has been shown to increase survival and improve long-term ventricular function.
In addition, in patients with dilated cardiomyopathy, the etiology of mitral insufficiency is the lack of coaptation of the valve leaflets from a dilated ventricle. The resultant regurgitation is due to the lack of coaptation of the leaflets. There is a growing trend to repair these valves, thereby repairing the insufficiency and restoring ventricular geometry, thus improving overall ventricular function.
Two essential features of mitral valve repair are to fix primary valvular pathology (if present) and to support the annulus or reduce the annular dimension using a prosthesis that is commonly in the form of a ring or band. The problem encountered in mitral valve repair is the surgeon's inability to fully assess the effectiveness of the repair until the heart has been fully closed, and the patient is weaned off cardiopulmonary bypass. Once this has been achieved, valvular function can be assessed in the operating room using trans-esophageal echocardiography (TEE). If the implant used to reduce the annulus is larger than the ideal size, mitral insufficiency may persist. If the implant is too small, mitral stenosis may result. In such cases, the surgeon must re-arrest the heart, reopen the heart, and then re-repair or replace the valve. This increases overall operative, anesthesia, and bypass times, and therefore increases the overall operative risks. The need exists, therefore, for an adjustable implant that would allow a surgeon to adjust the size and/or shape of annulus in situ in a beating heart under TEE guidance, or other diagnostic modalities, to achieve optimal valvular sufficiency and function.
Furthermore, it is not always possible to determine whether optimal valvular sufficiency and function has been achieved until some extended period of time after the valve has been repaired, and thus later adjustment of the implant may be needed. Also, there are instances in which mitral insufficiency reoccurs and further adjustment of the size and/or shape of the mitral valve becomes necessary. As a result, there also exists a need in the art for methods and systems that allow for the long term adjustment (i.e., months to years after implantation) of an implantable device, in a non-invasive manner.